1. Field of the Invention
The present invention generally relates to a method of detecting the end of the life of an image bearing member used in an image forming apparatus for forming an electrostatic latent image in an image bearing member by, for example, an electrophotographic system or an electrostatic recording system and visualizing the electrostatic latent image with a developer, to an image forming apparatus using the above method, and further, to a cartridge detachably attachable to the image forming apparatus.
Here, the image forming apparatus with the electrophotographic system include, for example, an electrophotographic copier, an electrophotographic printer (for example, an LED printer and a laser beam printer), and an electrophotographic facsimile.
The cartridge detachably attachable to the main body of the electrophotographic image forming apparatus includes a cartridge having at least one of an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, developing means for supplying a developer to the electrophotographic photosensitive member and cleaning means for cleaning the electrophotographic photosensitive member. In particular, a process cartridge is a cartridge in which at least one of the charging means, the developing means and the cleaning means, and the electrophotographic photosensitive member are integrally made into the cartridge, and the cartridge is made detachably attachable to the main body of the electrophotographic image forming apparatus, or a cartridge in which at least the developing means and the electrophotographic photosensitive member are integrally made into the cartridge and the cartridge is detachably attachable to the main body of the electrophotographic image forming apparatus.
2. Related Background Art
Conventionally, in an image forming apparatus of an electrophotographic system such as an electrophotographic copier or a laser beam printer, an electrophotographic photosensitive member functioning as an image bearing member is uniformly electrified by using charging means, and thereafter, the surface is irradiated with light corresponding to image information to form a latent image. Then, a developer is supplied to the latent image using developing means to visualize the latent image, and after the visualized image is transferred to a recording medium, the image is fixed in a fixing apparatus to obtain an image on the recording medium. Further, the electrophotographic photosensitive member after the transfer is cleaned with cleaning means.
In such an image forming apparatus, in order to attain a simple and easy exchange and maintenance of expendable supplies, such as the electrophotographic photosensitive member and the developer, a process-cartridge system is used in which an electrophotographic photosensitive member, developing means functioning as process means acting on the electrophotographic photosensitive member, charging means, cleaning means, a container for a developer, and a container for a waste developer are integrally made into a process cartridge, and the cartridge is detachably attachable to the main body of the image forming apparatus.
According to the cartridge system, a user can conduct maintenance of the apparatus without a serviceman. Images can be formed again by the user exchanging a cartridge when the developer has run out or when the photosensitive member drum has expired, for example. As described above, the cartridge system can remarkably improve operability of the apparatus, and thus, is widely used in the electrophotographic image forming apparatuses.
In the image forming apparatus of the cartridge system, for example, it is necessary for the user to exchange the cartridge at an appropriate time by notifying the user that the expendable supplies, such as the electrophotographic photosensitive member and the developer, have expired or that they are approaching the end of their life.
Conventionally, a first method of detecting the life of an electrophotographic photosensitive member having, for example, a cylindrical shape, that is, a photosensitive member drum comprises a method of detecting the end of the life of a photosensitive member drum by integrating the number of sheets on which an image formation operation is performed. In the simplest method, in the case where the size of the sheets of the recording medium, on which an image is formed, differs, for example, between the A4 size and the A3 size, the sheets of the recording medium are counted as the same. However, in this method, the precision of detecting the end of the life of the photosensitive member drum is not satisfactory. Further, using only the integration of the number of sheets on which an image formation operation is performed, the rotation time of the photosensitive member drum per one sheet of the recording medium differs depending on how many sheets are used for image formation per one job, that is, how many sheets of the recording medium are used for continuous image formation from the start of the image forming operation. Thus, the life of the photosensitive member drum varies in accordance with the rotation time, which is described later. Therefore, in this method, the precision of detecting the end of the life of the photosensitive member drum is not satisfactory.
Moreover, as described in Japanese Patent Application Laid-open No. 451259 as prior art, there is a second method of detecting the life of an electrophotographic photosensitive member comprising a method of detecting a charge amount of a photosensitive drum with a surface potential sensor. In accordance with this method, in actuality, a reduction of charge potential of the photosensitive member drum or a reduction of latent image contrast can be directly detected with the surface potential sensor. Thus, in comparison with the first method described above, end of life detection with satisfactory precision is possible, which reflects the state of an output image. However, in order to implement the above method, the surface potential sensor, an electric circuit for processing the output, and the like are needed, and thus, the cost increases. Further, with respect to a longitudinal direction of the photosensitive member drum, only the information on the photosensitive member drum corresponding to the sensor position is data to make a decision. Thus, the detection ability to detect a partial defect is weak, and this method is plagued by the variations in the surface potential sensor and the instability of change with time and the like. Therefore, this method is not necessarily a method of constantly detecting the end of the life of the photosensitive member drum with accuracy.
Furthermore, as a third method of improving the detection accuracy of detecting the end of the life of the photosensitive member drum while solving the problem of the first method, there is disclosed, in Japanese Patent Application Laid-open No. 5-188674, a method of integrating the rpm of the photosensitive member drum instead of integrating the number of sheets on which an image formation operation is performed. Based on the same principle, there is a method of integrating the rotation time of the photosensitive member drum. In any of these methods, since, with respect to one image formation operation, as the size of the recording medium becomes larger, the rpm (rotation time) increases while as the size of the recording medium becomes smaller, the rpm (rotation time) decreases, in accordance with the size of the recording medium, and the detection error of the end of the life of the photosensitive member drum due to the size difference of the recording medium becomes smaller in comparison with the case of integrating the number of sheets on which an image formation operation is performed. Further, the rpm (rotation time) of the photosensitive member drum is directly integrated irrespective of the number of sheets on which an image formation operation is performed per one job, and thus, the precision of the end of life detection is relatively satisfactory.
As a method which is developed on the basis of the above third method, there is disclosed, in Japanese Patent Application Laid-open No. 4-98265, a method in which the rpm of the photosensitive member drum at the time of actual image formation is integrated by integrating the rpm of the photosensitive member drum only at the time when a transfer charger functioning as transferring means operates so that the end of life detection of the photosensitive member drum with more accuracy is possible. Further, there is disclosed, in Japanese Patent Application Laid-open No. 6-180518, a method in which the rpm of the photosensitive member drum during an electrification process of the photosensitive member drum, and the rpm of the photosensitive member drum while a cleaning member contacts and cleans the photosensitive member drum, are respectively integrated, and the end of the life of the photosensitive member drum is determined on the basis of a comparison of the respective rpms and the setting values (life).
Further, the following method is known as a method of notifying a user of the proper timing for a process-cartridge exchange. Namely, in a method disclosed in Japanese Patent Application Laid-open No. 5-333626, the timing for the exchange of a process cartridge structured with a cleaner (cleaning means) and an electrophotographic photosensitive member is firstly notified to the user on the basis of the end of the life of the electrophotographic photosensitive member. That is, the apparatus is stopped at the time when the electrophotographic photosensitive member reaches the end of its guaranteed life by integrating the number of sheets of on which an image formation operation is performed and becomes unusable. Besides, as an exchange-display operation based on the end of the life of the electrophotographic photosensitive body, the apparatus urges a user to prepare a cartridge for exchange by displaying an indication that the exchange time and the guaranteed end of the useful life of the cartridge is approaching, or in a case where the cartridge is continuously used, the apparatus warns that the time to stop the use of the apparatus is approaching. Further, in accordance with this conventional technique, the apparatus is structured such that the user is notified of the time for a cartridge exchange also based on the toner capacity of a recovered toner containing portion of the cleaner. That is, the on-time of a driving motor for toner replenishment is integrated, and the apparatus is stopped in accordance with the earliest integration time which is expected to occur based on the worst conditions in which various variations are considered. Also in this case, the exchange-display operation based on the capacity in the toner containing portion comprises a display operation to prompt the user to exchange the cartridge at the time when the integration time of the on-time of the driving motor for toner replenishment becomes a certain value, and the display to notify the user that the time to stop the apparatus is approaching is made at a later integration time.
In this conventional technique, the operation based on the life of the electrophotographic photosensitive member and the operation based on the toner capacity in the recovered toner containing portion of the cleaner are generally set so as to have priority over the number of prints, that is, the life of the electrophotographic photosensitive member. However, when toner replenishment is frequently conducted because of an unusually high image density, and the recovered toner container is about to be filled earlier compared with the guaranteed life of (the guaranteed number of sheets) the electrophotographic photosensitive member, an action is taken based on the toner capacity of the recovered toner container.
Here, in the technique disclosed in Japanese Patent Application Laid-open No. 5-333626, the process cartridge is provided with storage means, the total electrification time of a primary electrifier provided in the image forming apparatus is collectively written in the storage means through a CPU provided in the image forming apparatus at the time of the exchange of the process cartridge, and also, the subsequent electrification time of the primary electrifier is written and stored in the storage means. Then, the storage means of the spent process cartridge is collected and analyzed, whereby the rpm of the photosensitive member drum at present, and the total amount of discharge time of a corotron and the like of the image forming apparatus in which the spent process cartridge has been used can be known with accuracy, and information collection to the image forming apparatus can be conducted at exchange intervals of the process cartridge. The above is disclosed. More specifically, the operation cycle number of the photosensitive member drum, the exchange time of an ozone filter, the abrasion (or wear) data prediction of the photosensitive member drum, and the like of the image forming apparatus at the time of the exchange of the process cartridge can be known.
However, the determination of the end of the life of the photosensitive member drum in the technique disclosed in this application is based on the number of sheets on which an image formation operation is performed in the end. As described above, there is no change in the lack of satisfactory precision in the prediction of the end of the life of the photosensitive member drum based on the number of sheets of image formation.
On the other hand, in recent years, as a developing apparatus for developing a latent image formed on an electrophotographic photosensitive member, there has been developed an apparatus in which so-called one-component developer, which substantially contains toner as its only constituent, is used. In this developing apparatus of a one-component developing system, a mixture of toner and a carrier, agitation, and control of the toner density (the ratio of the toner to the total amount of the toner and the carrier) are not necessary, which is dissimilar to a so-called developing apparatus of a two-component developing system. Thus, miniaturization of the apparatus and a low cost can be realized, and also, exchange of the developer becomes unnecessary, which is very effective in a printer or the like that is desired to be maintenance-free. If non-magnetic toner is used as the toner for the one-component developer, it becomes unnecessary to provide a developer carrying member for carrying a developer to an electrophotographic photosensitive member with a magnet roll. Thus, the miniaturization of the apparatus and a low cost can be further realized.
As the developing apparatus of a one-component developing system, there is known a so-called developing apparatus of a contact one-component developing system comprising: a developer container (hopper) for containing one-component developer (toner); a developer carrying member (developing roller) having a roller shape or the like for carrying toner to a latent image on an electrophotographic photosensitive member, which is provided adjacent to the developer container; a toner supply roller rotating in the same direction as the developing roller while contacting the developing roller; and developer layer thickness regulating means (regulating blade) having a blade shape or the like for regulating the toner amount carried on the developing roller, by which the toner in the hopper is carried to the developing roller by the toner supply roller, a toner thin layer is formed on the developing roller by the regulating blade, and the toner thin layer is made to contact the electrophotographic photosensitive member, to thereby develop the electrostatic latent image formed on the electrophotographic photosensitive member.
In a case where the non-magnetic toner is used as the toner for the one-component developer, the regulating blade, which is an elastic blade or the like, is made to contact the developing roller, and the Coulomb force due to charge of the toner or triboelectrification is utilized to form the toner thin layer on the developing roller, and thus, supplying and carrying of the toner are conducted.
Further, in recent years, a contact electrifier is widely being used instead of a corona electrifier, which has been conventionally widely used as an electrifier for performing an electrification process with an electrophotographic photosensitive member. The contact electrifier has many merits including a lower applied bias that is sufficient for the contact electrifier compared with the corona electrifier, the generation of a very small amount of ozone, a small number of required components that structure the electrifier, and a low cost for providing the electrifier.
Such a contact electrifier is roughly divided into a brush electrifier and a roller electrifier in accordance with the shape of a charging member to be used. The brush electrifier has problems involving a track of the brush, a bend of the brush in a case where the electrifier is made to contact the electrophotographic photosensitive member for a long period of time, and the like. On the other hand, the roller electrifier has difficult problems in that resistance regulation of the roller is necessary in order to obtain uniform electrification, in that contamination of the drum has to be prevented, which arises from bleeding of rubber that constitutes the roller, and in that there is a strict limitation on the shape, the surface property, and the like of the roller in order to obtain uniform electrification.
As the voltage applied to the contact charging member, only a DC bias (hereafter, referred to as “DC electrification”) and an AC bias superposed on a DC bias (hereafter, referred to as “AC electrification”) are used. Generally, there is a feature that the AC electrification enables uniform electrification compared with the DC electrification.
Examples of AC electrification include an electrification process in which a charging member having a roller shape (charging roller) is used as a charging member, and a DC voltage is superposed on an AC voltage which is twice or more as large as the voltage at the start of discharge of an applied bias (Japanese Patent Application Laid-open No. 63-149669 and Japanese Patent Application Laid-open No. 1-267667), an electrification process in which a conductive brush is used as an electrification member, and a DC voltage is superposed on an AC voltage which is twice or less as large as the voltage at the start of discharge of an applied bias (Japanese Patent Application Laid-open No. 6-130732), and the like.
The contact-electrification system described above has the merits that a small amount of ozone is generated, that the number of the required components that structure the electrifier are small, and that the electrifier is provided at a low cost. However, the damage to the electrophotographic photosensitive member is larger compared with corona electrification. In particular, this tendency is conspicuous in the case of using an OPC photosensitive member drum.
Further, even in the same contact electrification method, the damage to the electrophotographic photosensitive member varies according to the applied voltage to the charging member, and as the applied voltage increases, the damage to the electrophotographic photosensitive member becomes larger. In case that only the DC voltage is applied as an electrification bias, the damage increases in comparison with the case where the photosensitive member drum is rotated without applying the electrification bias. Moreover, it is found out that the damage (particularly, the abrasion amount of the OPC photosensitive member drum) further increases, and the damage is about several times as large as the damage in a case where only the DC voltage is applied as the electrification bias when the AC voltage superposed on the DC voltage is applied as the electrification bias.
In particular, if the AC voltage which is twice or more as large as the voltage at the start of discharge is applied, the phenomenon of damage to the electrophotographic photosensitive member becomes conspicuous. However, even if the AC voltage that is twice or less as large as the voltage at the start of discharge is applied, the damage is about several times as large as the damage in the case where only the DC voltage is applied.
Further, also in a case where the frequency of the AC voltage applied as the electrification bias is made larger, there is a tendency that the damage to the electrophotographic photosensitive member (in particular, the OPC photosensitive member drum) increases.
On the other hand, as described above, in recent years, there has been used a method in which a developing roller functioning as a developer carrying member is made to carry one-component developer, and the developing roller is made to contact a photosensitive member drum to develop an electrostatic latent image on the photosensitive member drum, but the photosensitive member drum is scraped by contact rotation of the developing roller as well.
In general, in a case where a one component non-magnetic developing apparatus is used, in which a developing roller contacts a photosensitive member drum, the peripheral speed of the developing roller is increased with respect to, for example, the peripheral speed of the photosensitive member drum in order to secure the required density. Particularly, in a case where the developing roller has a relative peripheral speed ratio with respect to the photosensitive member drum, there is a tendency that the damage to the photosensitive member drum increases.
However, in a color image forming apparatus in which an electrostatic latent image on a photosensitive member drum is developed by switching developing apparatuses of a plurality of colors, and in an image forming apparatus in which a spacing mechanism is provided for having a clearance between a developing roller and a photosensitive member drum, and a method of having a clearance between the developing apparatus and the photosensitive member drum during the rotation of the photosensitive member drum during a non-image formation period is adopted in order to prevent fog from arising as a result of contact development, the rotation time of the photosensitive member drum is not proportional to the contact time of the photosensitive member drum and the developing roller.
As apparent from the above description, in an image forming apparatus which is provided with the charging means that electrifies the photosensitive member drum with, for example, contact electrification under a plurality of electrification conditions during image formation and in which both the AC voltage and the DC voltage are used, the damage that the photosensitive member drum receives varies according to the electrification condition. Thus, with the conventional method of detecting the end of the life of the photosensitive member drum on the basis of only the rpm of the photosensitive member drum, it is difficult to predict the end of the life of the photosensitive member drum with accuracy.
Further, in a case where a developing apparatus which can be separated from the photosensitive member drum is used, the rotation time of the photosensitive member drum is not proportional to the contact time of the photosensitive member drum and the developing roller as described above. Thus, in the conventional method of detecting the end of life of the photosensitive member drum on the basis of only the rpm of the photosensitive member drum, it is impossible to predict the end of the life of the photosensitive member drum with accuracy.
Due to the above reasons, there is a fear that a warning for a cartridge exchange is not issued although the photosensitive member drum has expired to generate an image defect or that the warning for a cartridge exchange is issued although the photosensitive member drum has not actually expired yet.